1. Field of the Invention
The present invention relates to a control apparatus of a throttle valve in an internal combustion engine. More specifically, the present invention relates to a control apparatus of a throttle valve which can be operated by an electric motor.
2. Description of the Related Art
It is well known to control the speed of an automobile by depressing an accelerator foot pedal. The accelerator pedal is generally connected to a throttle valve in an internal combustion engine on the automobile by a cable or the like.
In contrast, it is also known to separate the throttle valve from the accelerator pedal, to provide a detecting means for detecting the degree of depression of the accelerator pedal, and to control the throttle valve by an electric motor in response to an output of the detecting means.
For example, Japanese Examined Patent Publication No. 58-25853 discloses a control apparatus of a throttle valve in an internal combustion engine, in which an electric motor controls a throttle valve through a control circuit which receives detection signals from an accelerator pedal position detector, a water temperature sensor and a throttle position detector. A problem in the motor driven control apparatus of a throttle valve as described in Japanese Examined Patent Publication No. 58-25853, is that it is necessary to provide a compensating device to ensure that the throttle valve is brought to an appropriate opening position, in the event that a malfunction of the throttle valve control motor occurs, in which case the engine could become uncontrollable.
Therefore, a clutch is provided between the motor and the throttle valve in this Publication. However, a further problem occurs in that the engine operation is stopped if a malfunction of the motor occurs.
Japanese Unexamined Patent Publication No. 59-122742 discloses a control apparatus of a throttle valve in an internal combustion engine with a compensating device, in which the apparatus includes a throttle valve with a spring biasing the throttle valve in the closing direction, an electric motor with an output wheel which is connected to the throttle valve via a cable and has a side projection, and an coaxial extra wheel connected to an accelerator pedal via a cable and having a side projection, the side projections being provided at angularly spaced positions. The extra wheel is rotatable relative to the output wheel. When the motor operates normally, there is no interference between the projections, and thus the motor can easily control the throttle valve through a control means. If the motor fails, the side projection of the motor output wheel are returned to the initial position in the anti-clockwise direction by the throttle return spring, while, by depressing the accelerator pedal, the side projection of the extra wheel can be turned in the clockwise direction to abut against the projection and ensure a minimum opening of the throttle valve. However, there is a still problem in the mechanism described in this publication in that the throttle valve cannot be opened until the accelerator pedal is further depressed, and the mechanism itself cannot work after the throttle valve is fully opened by the motor.
Also, Japanese Unexamined Patent Publication No. 59-190440, in an attempt to solve the same problems, discloses a control apparatus of a throttle valve, which includes a throttle valve with a throttle shaft, an electric motor connected to one end of the throttle shaft, and a compensating mechanism located at the other end of the throttle shaft. The compensating mechanism includes a segmental lever having a hub portion which is freely inserted over the throttle shaft, a small arm which is biased by a spring in a certain direction (valve closing direction), and a large segmental arm which is connected to the accelerator pedal by a cable. This segmental arm has a side projection, and the throttle shaft has a movable plate fixed at the end of the shaft. When the accelerator pedal is depressed, the segmental arm with the side projection is pulled, and the side projection moves away from the movable plate on the throttle shaft so that the motor can control the throttle valve in response to an output from an accelerator potentiometer. However, if the motor loses its control facility, the side projection of the segmental arm, by releasing the accelerator pedal, can abut against and force the projection back to the initial closed position of the throttle valve. There is, however, a problem in this mechanism in that the throttle valve cannot be opened again after it is once closed if the motor cannot output the control torque.